The object of the present invention is the production of assemblies formed of radial carcass tires and mounting rims, preferably "monobloc" rims, at least some of which may prove useful upon travel when the inflation pressure drops abnormally low as compared with the nominal pressure of use, known as the service pressure, the inflation pressure possibly even becoming zero.
The main difficulties encountered in the case of travel with a flat tire or with low pressure in the tire concern the risks of the unseating of the beads of the tire and, in particular, the unseating of the bead located on the outer side of the tire mounted on the outer side of the vehicle. The well-known techniques proposed in order to avoid such unseatings and, in particular, the one which consists of arranging a hump of small height axially to the inside of the outer rim seat, tend to increase the difficulties in mounting and removing the tires.
One solution which can be applied to the problem of the unseating of beads is that described in French Patent 1139619, which concerns an assembly formed of a tire and a rim which are of such a nature that the flexible edges of the tire, contrary to the usual beads, come, under the effect of the inflation pressure, to grip around rim stops intended to hold said edges spaced from each other. This solution requires a carcass reinforcement which is at least special and not in accord with the compromise of properties required for a modern tire.
Certain prior solutions recommend the addition to a rim, such as described above, of a tread support which is integrated or attached and fastened by any available means. Whether this be with hump or without hump, assemblies which comprise rims with tread supports are known, and German application 36 26 012 and French application 2 560 121 show such assemblies. However, they are not of general use, since, despite the advances made, difficult problems of mounting also arise. The above-mentioned French application describes a method of mounting which makes it possible to eliminate numerous difficulties, namely the swinging and ovalizing of one of the beads of the tire permit the passage of the rim, provided with its tread support within the tire, if said rim is presented with its axis of rotation perpendicular to the axis of rotation of the tire, the beads being then placed on their respective rim seats by means of mounting wells arranged axially on opposite sides of the tread support.
If one designates as S the overall width of the mounting rim measured axially between the ends of the two flanges, D.sub.J the diameter of the rim measured at the level of the intersection between the rim flange and the frustoconical generatrix of the rim seat, the latter being seen in meridian section, H' the height of the prop measured with respect to the parallel to the axis of rotation of the rim passing through said point of intersection, and D.sub.B the diameter of the bead of the tire, measured on a parallel to the equatorial plane of the tire, which parallel passes through the center of the bead wire, the method described above cannot be applied in the event that the amount 2 .pi.D.sub.B is less than 2(D.sub.J +2H'+S), hence the impossibility of having available tires of customary form ratio which have an effective inner tread support.
The difficulties in the mounting and removal of tires mounted on such rims are further accentuated by the introduction of modern tires with lower form ratio and furthermore frequently comprising greatly reinforced beads.